Carnegie Mellon’s Medium Energy Group: At the Forefront of Physics

Enter Room 8423 of Wean Hall and you encounter lathes, drill presses and other tools familiar to most machinists. But sitting nearby are recently milled parts whose purpose would mystify most of us. That is, unless you are a particle physicist. Welcome to Carnegie Mellon's Medium Energy Group (MEG). This team of scientists, students and technicians has been at the forefront of a unique field that hopes to bridge the gap between our understanding of everyday physical interactions and the activities of subatomic particles generated at extremely high energies.

"We’ve been among the trailblazers of medium energy physics," says Gregg Franklin, professor of physics who joined MEG in 1981.

A Culture of Collaboration

For 38 years, the MEG group has been constructing electronic components and detectors used to identify and analyze subatomic particles generated within other instruments called accelerators.

"We are known for building stuff," said Brian Quinn, a professor of physics who joined the group in 1988. This "stuff" includes not just detectors and electronics, but support systems and software.

While most universities involved in medium energy physics research outsource construction of their equipment, Carnegie Mellon can make immediate turnarounds on equipment and prototypes, according to Gary Wilkin, the MEG's full-time laboratory technician.

“By keeping everything in-house, we can control quality unlike any other facility,” explains Wilkin. “If one of the professors wants to change something, or add something else, they just walk across the hall.”

Designing and building experimental components is essential to MEG's international leadership in research to understand the subatomic fabric of matter. This group ships MEG-built equipment to facilities around the world for use in experiments by research teams. In the past, the MEG has provided equipment and conducted studies at CERN (the French acronym for the European Organization for Nuclear Research) in Switzerland and Brookhaven National Labs in New York. Currently, the group centers most of its activities at the Thomas Jefferson Accelerator Facility, or Jefferson Lab, in Newport News, Va.

A New Physics Era

Enter any of the Jefferson Lab’s three experimental halls and you find complex detectors and experiments designed, at least partly, by Carnegie Mellon’s MEG. Jefferson Lab houses a continuous-wave electron accelerator that bombards a target with a hair-thin stream of electrons. This instrument allows researchers to collect much more data than previously possible to investigate quarks, the small particles that make up more familiar protons and neutrons. Medium energy experiments also generate fleeting combinations of quarks, such as mesons (made of two quarks) and the recently described "pentaquark." Using the Jefferson Lab's accelerator and their custom-built, high-precision detectors and electronics, the MEG is pioneering studies of quark interactions and the formation of such rare particles, called "exotics."

Hall B houses a highly specialized detector that includes a multi-million dollar drift chamber, which was designed and machined in the MEG labs at Carnegie Mellon and pieced together in clean rooms at the University of Pittsburgh. The chamber consists of tens of thousands of wires that energize when charged particles hit them. The chamber played a critical role in 2001, when researchers in the MEG and at Jefferson Lab found possible evidence for the pentaquark, first identified by a Japanese research team.

"This opens up a whole new category of particles and interactions," explains Reinhard Schumacher, professor of physics who joined the MEG in 1987 and is a former spokesperson for the Hall B experiment. Future MEG investigations at the Jefferson Lab will investigate the pentaquark’s properties.

In Hall C, the MEG is involved with G0, which measures how the strange quark (named for its previously observed peculiar behavior) contributes to the overall properties of a proton. The G0 Collaboration brought in the MEG to construct half of the G0 detector and its high-speed data acquisition electronics. The MEG had to integrate their work closely with that of a French team building the other half of the detector.

“The design of these electronics was the most challenging we had even seen,” says Quinn, who serves on the G0 Collaboration’s Executive Board. The first scientific data runs using these electronics and detector will finish soon.

Future Studies

On the horizon, the MEG plans to build part of the forty-million dollar, 3500-piece detector for Jefferson Lab's projected GlueX experiment, an international project to study how quarks bind within mesons via tubes of energy called gluons.

“The GlueX experiment will try to excite these tubes by making them rotate and then investigate if this, in turn, creates new, exotic types of mesons,” says Meyer, who serves as the deputy spokesperson for GlueX, which recently received federal notice to move forward.

Other projects are also in the works as the MEG continues to adapt and contribute to the changing boundary of medium energy physics.